1. Field of the Invention
The present invention relates to hemming units and apparatus that are used for hemming workpieces that may be formed into parts of various machines and apparatus, such as doors, hoods and trunk lids of automobiles.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 7-232220 teaches a hemming apparatus that includes a press machine. An upper die and a lower die are mounted on the press machine. The upper die has a pre-hemming tool and a finish hemming tool. In order to hem a workpiece, the workpiece is positioned on the lower die, and then the upper die is lowered by the press machine by means of a press slide mechanism. As a result, the workpiece can be hemmed by the operation of the pre-hemming tool and the finish hemming tool. Further, in order to increase the number of workpieces that can be hemmed at one time, hydraulic cylinders may be optionally incorporated as auxiliary drive sources. However, because this type of hemming apparatus requires a press machine, a large-scale installation, including a pressing machine and upper and lower dies, is required. Therefore, installation costs are relatively high and a large installation space is required.
It is, accordingly, one object of the present invention to teach improved hemming units and apparatus that can be, e.g., installed at a lower cost and in a smaller space without sacrificing operability.
According to one aspect of the present teachings, hemming units are taught that comprise a hemming tool, an actuator for moving the hemming tool, and a link mechanism connecting the actuator and the hemming tool. In a representative embodiment, the link mechanism may include a parallel link mechanism and a toggle link mechanism. If the link mechanism is utilized in order to transmit the actuator force to the hemming tool, the actuator force can be amplified to apply an appropriate pressing force against the workpiece via the hemming tool. Therefore, the hemming tool may have a simple construction and can be manufactured at a relatively low cost.
In another representative embodiment, the hemming tool may be operated in a first mode for a pre-hemming operation and in a second mode for a finish hemming operation. Therefore, the pre-hemming operation and the finish hemming operation can be performed using the same hemming unit. Thus, it is not necessary to incorporate two separate hemming units that are respectively used for the pre-hemming and finish hemming operations. As a result, the manufacturing costs and the installation space can be substantially reduced.
Preferably, a chucking arm is connected to the toggle link mechanism, so that the chucking arm can apply a pressing force to a workpiece support that supports the workpiece in a direction opposite to the direction of the pressing force that is applied to the workpiece by the hemming tool. Because no substantial force is applied to the workpiece support to deform or bend the workpiece support, the workpiece support is not required to be highly rigid or have a large thickness in order to support the workpiece. Therefore, the workpiece support and its support legs as well as a base, on which the support legs are placed, may be relatively light weight. In addition, if the actuator that drives the hemming tool by means of the toggle mechanism actuates the chucking arm, an additional actuator is not required to actuate the chucking arm. Thus, manufacturing costs can be further reduced.
According to another aspect of the present teachings, hemming apparatus are taught that comprise, in addition to the hemming unit, a workpiece support for supporting the workpiece during a hemming operation, and a workpiece holder for holding the workpiece in position relative to the workpiece support.
In another representative embodiment, the hemming apparatus may include a plurality of hemming units that are disposed adjacent to the periphery of the workpiece support.
Additional objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.